Scanning laser obstruction detection system utilizing a retroreflective strip



March 10, 1970 c. w. RENO ETAL 3,500,063

SCANNING LASER DESTRUCTION DETECTION SYSTEM UTILIZING A RETRDREFLECTIVE STRIP Filed June 10, 1968 \IIII I I I .ll. llllllllllllllllllIllllll a m 3 H l I w :w 5 D l O W a T v 3 f1? A0410 Z T 4 E V 2 m m [U M 14 RM 2 I w a 3 n v \lflwl b ullll'll-lllllllllllllllnllllllllllllll llll [NYE/V70? ILUQM RENO QME TAIZZQISMI CHAILLEs IZIm-mrw y la/Ma mum-- United States Patent U.S. Cl. 250-217 '10 Claims ABSTRACT OF THE DISCLOSURE A system for detecting an obstruction in a given area utilizing a laser beam is disclosed. A laser beam is scanned over the area towards a retro-reflective target strip and returned to a receiver located proximately to the transmitter. If an obstruction is detected in the area, a signal is produced giving notice of the obstruction.

This invention relates to a system for detecting an obstruction in an area to be protected, and more particular ly, a system utilizing the advantages of a laser beam for detecting obstructions along a railroad track.

Due to the increase in population and urbanization, a high-speed rail transportation system is being developed in which a train will travel upwards of 250 miles per hour. At this speed even a small object along the rail can cause a train wreck resulting in massive injuries and loss of life. Therefore, it is important that together with these trains, some sort of system be developed for detecting obstructions on the right-of-way.

An object of this invention is to provide a system for detecting small obstructions in a protected area.

This system utilizes a laser beam transmitter, retro-reflective means scanned by the laser beam and a laser beam receiver arranged so that the laser beam scans across the protected track area and is returned to the receiver in the event no obstruction is present on the track. When no beam or a beam modified by an obstruction is returned to the receiver, an alarm signal is produced, for example, which activates the necessary controls to stop a train running on the track in suflicient time to avoid the obstruction.

The invention is more particularly defined in the following figures and detailed description wherein:

FIGURE 1 is an overhead view of a railroad track showing the positions of the transmitters along the track for one embodiment of this invention;

FIGURE 2 is a more detailed diagram of the laser transmitting and receiving means which is shown in FIGURE 1; and

FIGURE 3 is a view taken perpendicular to the track showing the placement of the transmitting and receiving and the target means in a second embodiment of this invention.

Referring to FIGURE 1, a monorail track is shown with flat beds 12 and 14 on either side of the track 10. Laser beam transmitting and receiving apparatus 16, 18 and 20 are spaced a certain distance apart on the side of bed 14 so that the transmitted beams scan across the beds 12, 14 and the track 10. A retro-reflective target strip 22 is positioned on the side of the bed 12. As understood in the art, a retro-reflective target strip is one whereby a beam of light is transmitted to the strip along a path which is at any angle, within certain limits, with respect to the strip, and returned along the same path to the transmitting means.

In FIGURE 1, the three transmitting and receiving apparatus 16, 18 and 20 are identical, and each one is designed for scanning an angular area of approximately 140 3,500,063 Patented Mar. 10, 1970 degrees. This is because the smallest angle between target 22 and the incident path of the beam for which the target 22 will normally return a beam along the incident path is degrees. Each of the apparatus 16, 18 and 20 are further constructed so that they rotate in effect through an angle of 140 degrees about an axis perpendicular to the beds 12 and 14, whereby the transmitted and reflected laser beams travel parallel to beds 12 and 14. Throughout each scan, a laser beam is transmitted from the transmitter part of apparatus 16, 18 and 20 across the protected area to target 22 and thereupon returned to the receiver part of apparatus 16, 18 and 20.

Referring to FIGURE 2 wherein a detailed description of one example of each of the transmitting and receiving apparatus 16, 18 and 20 is shown, a laser beam transmitter 24 transmits a laser beam along path 26 as shown.-A

fixed reflector 28 reflects the laser beam along path 29 towards a scanning reflector 30 which in turn reflects the beam along path 31 towards target 22. As the beam travels along path 31 to and from target 22, it expands slightly due, for instance, to dust in the air or inaccuracies in target 22. By the time the laser beam hits target 22, it is somewhat larger than it was at the time it left transmitter 24. The beam is reflected from target 22 back along the same path and by the time the beam reaches the scanning reflector 30, it is much larger than it was when the beam was reflected from reflector 30 towards target 22. In FIG- URE 2 the return beam path is shown as being between lines 32, 32. When the return beam hits reflector 30, it is reflected back along path 33, the center of which is parallel to path 29. A focusing lens 34 is positioned so that path 33 intersects it. However, fixed reflector 28 is also intersected by path 33 before it reaches lens 34. When reflector 28 is made much smaller than path 33, as shown in FIGURE 2, much of the laser beam in path 33 still intersects lens 34.

Laser beam receiving and translating apparatus 36 is positioned at the focal point of lens 34 so that the portion of the beam intersecting lens 34 is applied to a receiver opening 37 in the apparatus 36. Apparatus 36 translates the laser beam into an electrical signal by any known suitable optical detecting means, not shown, and a record is made in the recorder and comparator 38 of this signal for each scan. On each successive scan, the received signal is compared with the previously received signal, and if there is any deviation between the two, a signal is transmitted, for example causing a train traveling over the track 10 to be stopped while notifying maintenance personnel of the obstruction. A mechanical linkage represented by dashed line 39 or other suitable coupling means is provided to synchronize the operation of the recording and comparing means 38 with the scanning cycle of the scanning reflector 30 to provide for the proper comparison of the received signals from the receiver 36 on a scan-by-scan basis. Moreover, recorder and comparator 38 can be programmed so that if the train is the obstruction causing the deviation, no signal for stopping the train is transmitted. Such a program might provide that no signal is transmitted if the obstruction goes away. At the same time, a separate signal could be transmitted notifying the rail terminal of the exact location of the train at all times, and hence provide a track signal control system as well as obstruction detection. L

In FIGURE 3, a system is shown in which protectlon is given to each of the flat beds 12 and 14, as well as over the rail 10. Three transmitting and receiving apparatus 40, 42 and 44 are used to scan a designated area. Apparatus 40 and the reflector 22 operate as described above in connection with FIGURE 1. Apparatus 42 and 44 operate in the same manner over an identical angular area but only cover the area of a respective flat bed. Retroreflective target means 46 and 48 are positioned along each vertical side of track 10, and operate in the manner of the retro-reflective target 22 to return the scanning laser beams to the respective apparatus 42, 44.

What is claimed is:

1. In combination,

means for generating a laser beam,

a fixed reflector for reflecting said beam along a given path,

a rotating scanning reflector positioned in said path for reflecting said beam received from said fixed reflector,

said scanning reflector having a reflective area larger than the dimensions of said fixed reflector perpendicular to said path so that upon the scanned laser beam returning to said scanning reflector from a reflective object with the returned beam having a cross-sectional area larger than that of the beam reflected towards said object, the returned laser beam is reflected back along said path with a cross-sectional area larger than said dimensions of said fixed reflector, and

a laser beam receiving means positioned to receive that portion of said returned laser beam reflected along said path by said scanning reflector Which is unobstructed by said fixed reflector.

2. The invention according to claim 1 wherein said reflective object is a retro-reflective target:

3. The invention according to claim 1 wherein said laser beam receiving means further includes means for translating said returned laser beam, during each scan into a signal dependent upon said returned laser beam, means for comparing said translated signal with a predetermined signal and for providing a further signal when there is a difference between said translated signal and said predetermined signal.

4. The invention according to claim 3 wherein said predetermined signal corresponds to a translated signal from a previous scan of said scanning reflector means, and wherein the frequency and phase of said scans are identical.

5. A scanning laser beam obstruction detection system for detecting the presence of an obstruction in an area to be protected, said system comprising,

"a scanning'reflector means,

a laser beam transmitting means for transmitting a laser beam which expands in cross-sectional area and which is reflected by said fixed reflector along a given path, the dimensions of said fixed reflector perpendicular to said path being smaller than the dimensions of the reflective area of said scanning reflector perpendicular to said path,

said fixed reflector and scanning reflector means being so positioned that said laser beam reflected from said fixed reflector is applied along an unobstructed path to said scanning reflector means and reflected thereby along a scanned path over said area,

reflective target means which intersects said scanned path and which operates to return said laser beam received from said scanning reflector means back along said scanned path towards said scanning reflector means so that said returned laser beam is reflected by said scanning reflector means back along said first mentioned path, and

laser beam receiving means positioned to receive that portion of said returned laser beam not obstructed by said fixed reflector which is applied from said reflective target to said scanning reflector means and reflected thereby along said first mentioned path.

6. The invention according to claim 5 wherein said scanning reflector means includes means for rotating said scanning reflector means about an axis located substantially at the center of said given path.

7. The invention according to claim 5 wherein said reflective target means is a retro-reflective target strip.

8. The invention according to claim 5 wherein said laser beam receiving means further includes means for translating said returned laser beam into a signal dependent upon said returned laser beam, means for comparing said translated signal with a predetermined signal and for providing a further signal when there is a difference between said translated signal and said predetermined signal.

9. The invention according to claim 5 wherein said predetermined signal corresponds to a translated signal from a previous scan of said scanning reflector means and wherein the frequency and phase of said scans are identical.

10. The invention according to claim 9 in which said previous scan is the immediately preceding scan of said reflective scanning means.

References Cited UNITED STATES PATENTS 11/1956 Sick 250-221 12/1967 Miiller 250221 US. Cl. X.R.

Disclaimer 3,500,063.0harles William- Renon, Haddonfield, NJ. and Richard James Tarzaiski, Philadelphia, Pa. SCANNING LASER OBSTRUCTION DETECTION SYSTEM UTILIZING RETROREFLECTIVE STRIP. Patent Mar. 10, 1970. Disclaimer filed Aug. 8, 1977, by the assignee, RC'A Corporation. Hereby enters this disclaimer to the remaining term of said patent.

[Ofiioial Gazette October 4, 1977.] 

